While we were visiting a friend in his home (lucky us, he had invited us for one of his fantastic brunches), he asked about the purple string beans:  Do they, he wondered, taste any different from the green ones?

It is a good question.  Purple is an unusual color in the vegetable garden, second only to blue in rarity (is there any blue comestible other than blueberries?).  And while color is not always an indicator of flavor—the taste of red and green apples is not that different, for instance—it can be, especially when the color difference is due to ripeness, or lack thereof.

The answer to our friend’s question, though, is:  No; the purple string beans taste more or less the same as do the green ones.  In fact, as the beans cook, the purple fades away, leaving only the familiar green tint.  This is because heat and loss of acidity (due to dilution in neutral water) break down the anthocyanins that produce the color purple.  Chlorophyll, the green pigment (and component of photosynthesis), is apparently more stable.  (If we grow the purple string beans again next year—which is likely—I might try cooking a batch in vinegar or lemon juice to see whether that preserves the purple color.)

That matter resolved, I’ll ask my own follow-up questions:  What about the other vegetables growing in our garden?  Does their color dictate the flavor?

Well, as an indicator of ripeness, sure.  An unripe green tomato has a vastly different taste compared to a ripe red one.  We don’t grow them here, but apples (and most other fruits) exhibit this property.  It should be noted, however, that not all vegetables change color as they ripen.  Eggplant, for instance, starts purple and stays purple throughout its growth (and even its blossoms are tinged with purple).

But what about different colors of ripe tomato?  Do the yellow and orange varieties have a different flavor from the traditional red ones?  How about tomatoes that are green when ripe?  Furthermore, are the differences in flavor, if any, due to the color or is the color just an indicator of the difference?

Answering the last question first, I think the color is merely an indicator of a difference in flavor and not the cause of it.  The various colors of tomato do have varying flavors but the variations are due to different levels of sugar and acidity.  And as noted above, pigments react very differently to acidity.  Typical red tomatoes are relatively high in acidity so acid-resistant pigments like carotenoids (of which lycopene is the most common in tomatoes) will dominate their color.

At the other end of the spectrum (in both flavor and color), orange, yellow, green and purple (sometimes referred to as black) tomatoes are sweeter in flavor, a result of their being lower in acid.  Another consequence of higher pH is that pigments less resistant to acid, such as the anthocyanins, can survive in their colored state and contribute to the tomatoes their distinctive hues.  In other words, the pigments act as a natural litmus test to visually signify flavor.

This is only a quasi-scientific analysis but it makes sense, at least for the tomatoes.  In addition to the tomatoes, we also planted different colors of carrots, radishes, beets and bell peppers this year.  To my taste buds, the red and white-striped Chioggia beets tasted the same as the Touchstone Gold and neither tasted any different from the typical all-red variety.

Similarly, there was only one significant difference between the taste of our Quadrato d’Asti Rosso (red) and Orange Sun (guess) bell peppers and the common green variety.  The peppers we grew tasted less grassy, a flavor component that I can only call “green”.  This is a good thing because that grassiness usually puts me off bell peppers.

Our radish crop was not sufficiently successful to make an assessment of their flavors but the carrots, which flourished a wide rainbow of colors, also yielded an array of flavors.  The orange were the most typical (no surprise there) while the yellow and white were woodier and the purple were sweeter.  The range in flavor was not quite as great as in color or as stark as with the tomatoes but there was definitely a correlation.